Numerous processes for the preparation of polyurethanes which are soluble or dispersible in water are known and are described for example in U.S. Pat. Nos. 3,479,310; 3,756,992; 3,920,598; 3,905,929; 4,092,286 and 4,108,814; British Pat. No. 1,076,688 and German Offenlegungsschriften Nos. 2,446,440; 2,551,094 and 2,555,534. Further improvements to these known processes constitute the subject matter of German Patent Applications Nos. P 26 51 505 which corresponds to U.S. Pat. No. 4,238,378; P 26 51 506 which corresponds to U.S. Pat. No. 4,237,264; P 26 59 617 which corresponds to U.S. patent application Ser. No. 862,455, filed Dec. 20, 1977; P 27 21 985 which corresponds to U.S. Pat. No. 4,182,828; P 27 25 589 which corresponds to U.S. patent application Ser. No. 908,885, filed May 24, 1978; P 27 30 514; P 27 32 131 which corresponds to U.S. Pat. No. 4,192,937; and P 27 34 576 which corresponds to U.S. Pat. No. 4,240,942.
These processes known in the art relate both to the preparation of ionically modified polyurethanes as described for example in U.S. Pat. Nos. 3,479,310 and 3,756,992 and British Pat. No. 1,076,688, to the preparation of non-ionically, hydrophilically modified polyurethanes as described for example in U.S. Pat. Nos. 3,920,598 and 3,905,929 and to the preparation of polyurethanes containing ionic groups and non-ionic hydrophilic groups as described for example in U.S. Pat. No. 4,092,286 and German Offenlegungsschrift No. 2,551,094. These polyurethanes, in particular those described in the last mentioned Offenlegungsschrift and U.S. Pat. No. 4,092,286, have numerous important advantages. In spite of containing ionic groups, they are largely insensitive to electrolytes and have excellent frost-resistance. In addition, the authors of German Offenlegungsschrift No. 2,551,094 and U.S. Pat. No. 4,092,286 found that if the polyurethanes contained both ionic and non-ionic hydrophilic groups, a much smaller concentration of hydrophilic groups was sufficient to ensure their dispersibility than that required when ionic groups or non-ionic groups were incorporated alone.
The process according to the invention described below constitutes an improvement of the process according to German Offenlegungsschrift No. 2,551,094 and U.S. Pat. No. 4,092,286 in that hydrophilic starting components which contain both sulphonate groups and ethylene oxide units which are arranged within a polyether chain are used for the first time. In the process according to German Offenlegungsschrift No. 2,551,094 and U.S. Pat. No. 4,092,286, the introduction of these different hydrophilic groups still necessitated the simultaneous use of both starting components which contained ethylene oxide units and other starting components which contained ionic groups. Since both these hydrophilic starting components used according to German Offenlegungsschrift No. 2,551,094 and U.S. Pat. No. 4,092,286 consist not only of the aforesaid hydrophilic groups, but also of structural units which constitute a considerable proportion by weight and contribute nothing to the dispersibility of the polyurethane, it is necessary to incorporate a large quantity of hydrophilic starting components into the polyurethane in order to introduce the number of hydrophilic groups required to render it dispersible or soluble. This so-called "ballast" which is superfluous for the purpose of dispersibility and often has a deleterious effect on other properties of the polyurethanes is reduced to an absolute minimum in the process according to the invention described below since in this process both ionic groups (sulphonate groups) and non-ionic hydrophilic groups are incorporated by means of a single hydrophilic starting component which contains both centers.